The invention relates to a control apparatus.
Furthermore, the invention relates to a network node. The network node can be used to set up a data network (for example for automation, medical, transport or traffic applications). The terms network node and data network node are also customary for network nodes. A data network can be regarded as a (digital) communication network.
In addition, the invention relates to a method for interchanging data via a data network to which a first and a second data terminal device are connected, wherein the data network has a multiplicity of network nodes and network nodes in a multiplicity of pairs of the network nodes are respectively connected by means of at least one transmission link. Data that are interchanged via the data network can also be referred to as messages. The data are usually transmitted on a packet-by-packet basis, that is to say in data packets, which are also referred to as telegrams or data telegrams.
In order to improve an availability of installations (for example industrial installations), installation parts are designed to be redundant. Such installations can require that a temporary interruption in a data transmission owing to a technical fault in a single network component (single point of failure) lasts no longer than one processing cycle of a control application in the installation. The length of a processing cycle is typically shorter than 1 ms. A distinction is drawn between media redundancy and system redundancy. In order to ensure media redundancy, layer 2 data networks are set up in parallel or ring structures are used.
For each of the two media-redundant topologies, a respective protocol has been standardized in the international standard IEC 62439-3, Industrial communication networks—High availability automation networks—Part 3: Parallel Redundancy Protocol (PRP) and High-availability Seamless Redundancy (HSR). The Parallel Redundancy Protocol (PRP) supports parallel data networks. The High-availability Seamless Redundancy protocol (HSR protocol) supports ring structures.
A common feature of both protocols (PRP, HSR) is that high-availability time-critical data from a first terminal station are (duplicated and) supplied to the data network via different network accesses and are then transmitted to a second terminal station in parallel via disjunct data paths in the data network. At the second terminal station or at an output coupler, duplicates (redundant packets) are filtered out. The transmission of high-availability and time-critical data packets via disjunct parallel data paths is used to ensure seamless redundancy through the medium. This means that no reconfiguration time is required after an interruption (a temporary failure) in one of the data paths (or the network nodes). Even after an interruption in one of the data paths has been removed, no reconfiguration time is required. Two data paths are disjunct with respect to one another if they have no shared transmission links.
PRP requires two separate data networks that must not be connected to one another via network couplers (for example bridges).
HSR has a similar problem when rings are connected via network couplers. If the ports on the ring coupler are inadvertently transposed, for example, the two rings can fuse into one large ring. Furthermore, neither the HSR protocol nor the PRP protocol provides for overload protection.
In order to guarantee ring separation (as is necessary for HSR) or data network separation (as is necessary for PRP), setup guidelines are issued. However, this does not ensure (in a technical, intrinsic manner) that such setup guidelines are also observed. It is known practice to monitor observance of setup guidelines using data network monitoring, however.
The need for network-dedicated overload protection is avoided today through careful project planning by ascertaining expected volumes of data traffic and using organizational measures to ensure that network nodes for which there is no provision in the network planning are not connected. Data networks that have undergone such project planning are also referred to as ‘engineered networks’. A disadvantage of this approach is that expected volumes of data traffic in the data network need to be known. This complicates scalability for such data networks.